I’ve only been playing since June and I have Chewbacca and you don’t. So consider me a bounty hunter expert.
I completed 7-Star Chewbacca in a few attempts with Gear 12 Bossk, Fett, Greedo, IG-88 and Gear 11 Dengar. Double Zeta Bossk, Zeta Fett, ig-88 and Greedo. Dengar Zeta seems unnecessary.
Greedos stun zeta proves useful especially against Chewbacca who I recommend using it on. Han seems to resist it every time.
Even though Leia is weaker, kill Lando first because Leia is Guarded by Chewie and Lando is not. Chewies not a big Lando fan.
After Lando perishes, go for a burst damage quick kill on Leia.
Next kill Chewbacca as he’s Guarding Han and Han is not as squishy as you’re used to him being.
Once Han’s lifelong furry friend and life debt slave has been defeated in battle you can proceed to vanquish Han from the paradise of cloud city.
Finally R2 - the tankiest of them all - can now be defeated. His stealth won’t be an issue with Dengar. Also use Dengars stuns on Chewbacca.
Remember, Bossk is vital. Save your aoes for when he needs protection recovery as per usual.
Hope this helps.